Facebook experiment upsets regulators

European regulators are concerned Facebook may have breached data protection laws with a controversial 2012 study that played with the mood of its users.

Officials in the U.K. and Ireland, where Facebook(FB, Tech30) has its European headquarters, are asking questions of the company after details of the experiment were published last month, angering many users.

"We are awaiting a comprehensive response on issues raised," said a spokesperson for the Irish data protection commissioner.

Facebook changed the content mix in the News Feeds of almost 690,000 users to gauge their emotional response to positive or negative posts.